Overhead and jib cranes that can be driven to move a lifted load in a horizontal direction.
Suggestions have been made for power-driven cranes to move a hoisted load laterally in response to manual effort applied by a worker pushing on the lifted load. A sensing system determines from manual force input by a worker the direction and extent that the load is desired to be moved, and the crane responds to this by driving responsively to move the lifted load to the desired position. Examples of such suggestions include U.S. Pat. Nos. 5,350,075 and 5,850,928 and Japanese Patent JP2018293.
A problem encountered by such systems is a pendulum effect of the lifted load swinging back and forth. For example, as the crane starts moving in a desired direction, the mass of the load momentarily lags behind and then swings toward the desired direction. A sensing system included in the crane can misinterpret such pendulum swings for worker input force. This can result in the crane driving in one direction, establishing a pendulum swing, sensing that as a reverse direction indicator, and driving in the opposite direction, causing a dithering motion. In effect, by misinterpreting pendulum swings as worker input force, the crane can misdirect the load in various ways that are not efficient or ergonomically satisfactory.
The inventive solution involves a sensing pendulum arranged above a hoist for the crane and a sensor for determining the load lifted by the hoist. The load sensor is preferably a load cell or strain gauge incorporated into the sensor pendulum. Arranging a sensor pendulum above the hoist provides some beneficial mechanical damping of pendulum effects from the hoist swinging below the sensing pendulum and the cable or rope and load swinging below the hoist. Two pendulum links below the sensing pendulum, including the hoist and load, divide or distribute pendulum effects and make them less evident to motion sensors arranged above the hoist to respond to the sensing pendulum. Crane control software receiving lateral load movement information from X and Y sensors arranged above the hoist, along with information on the mass of any load suspended from the hoist, can better distinguish between worker input force and consequential movement of the pendulum links below the sensor pendulum.
The invention thus involves arranging a sensor pendulum and associated X and Y sensors above a crane hoist while also sensing the mass of any load suspended from the hoist. Such a mechanical arrangement of motion and load sensors enables a crane control system to derive more reliable information on worker input force to the load and more reliably drive the crane in a desired direction to move a hoisted load to a position indicated by a worker. Preparing suitable software for driving the crane in response to worker input is made easier by suspending the hoist from a sensing pendulum that senses load mass and supplying load motion signals to crane control software from sensors detecting movement of the pendulum above the hoist.